docs: def abs(f=Ellipsis):
      '''
      abs() yields a potential function equivalent to the absolute value of the input.
      abs(f) yields the absolute value of the potential function f.
  
      Note that abs has a derivative of 0 at 0; this is not mathematically correct, but it is useful
      for the purposes of numerical methods. If you want traditional behavior, it is suggested that
      one instead employ sqrt(f**2).
      '''
      f = to_potential(f)
      if is_const_potential(f): return const_potential(np.abs(f.c))
      elif is_identity_potential(f): return AbsPotential()
      else: return compose(AbsPotential(), f)